The invention relates to a control system for a synchronous machine and a method for operating a synchronous machine.
When controlling a synchronous machine, for example in an electrical drive system of an electrically operated vehicle, the acquirement of the relative position of the rotor to the stator of the synchronous machine plays a key role. In order for a synchronous machine to provide a required torque, a rotating electrical field is generated in the stator which rotates synchronously with the rotor. The current angle of the rotor for the feedback control is required for the generating of this field.
An option for determining the rotor angle is to feed test voltage signals into one or a plurality of phases of the synchronous machine and to measure the system response by evaluating the phase currents at the neutral point of the synchronous machine in order to draw conclusions therefrom about the current rotor angle.
The WIPO patent publication WO 2009/136381 A2 discloses, for example, a method for determining the rotor angle of a synchronous machine in which measuring periods for measuring voltages at the neutral point are optimized by shifting clock samples of a pulse width modulated phase actuation. An exemplary test signal injection method for three-phase machines is revealed in Linke, M et al.: “Sensorless Speed and Position Control of Synchronous Machines Using Alternating Carrier Injection”, Electric Machines and Drives Conference, IEMDC 2003, IEEE. The German patent publication DE 10 2006 046 638 A1 ultimately discloses a further test signal method for determining items of phase position information of a rotor of a synchronous machine.
Many of these sensorless methods are based on entering phase-shifted voltage pulses, which utilize the anisotropy of a synchronous machine in order to obtain an item of rotor position information from the different system responses. Depending on the feed of useful current to the synchronous machine, a decrease in said anisotropy may occur at certain operating points so that the rotor position information can no longer be extracted or at least no longer be extracted with sufficient reliability from the data. In order to expand the application range of sensorless methods, there is therefore the need for solutions with regard to the actuation of a synchronous machine, which can provide better boundary conditions for the reliability and stability of methods for determining rotor angles.